Polymer concrete (PC) is a well-known industrial material used for many infrastructure applications including bridge deck overlays, manholes, coating layers for metallic pipelines, repair for existing concrete structures, grout for post-tensioning ducts, machine foundations, etc.
In addition, polymer concrete (PC) overlays are typically used in infrastructure applications, specifically bridges and parking structures, to provide durable protection to the structural system against corrosion. However, PC suffers from cracking and crack propagation during its service life mostly due to fatigue. Fatigue cracking of PC results in limiting the service life of PC considerably. Monitoring of fatigue damage in PC can help extend PC service life.
Polymer concrete (PC) is also a composite material in which a polymer matrix such as epoxy, unsaturated polyester (UP), vinyleseter, or methyl methacrylate (MMA) replaces Portland cement as a binder to bond aggregate together. PC is used in numerous applications including bridge deck overlays, machine foundations, sewer manholes, pipes and pipe liners, hazard materials storage and architectural panels. PC gained worldwide attention in the construction field since the 1970s because of its superior durability and attractive mechanical properties.
Typical mechanical properties of PC incorporate a compressive strength of 50-100 MPa, a tensile strength of 8-10 MPa, a flexural strength of 20-24 MPa and a wide range of modulus of elasticity in the range of 20-40 GPa depending on the type of resin and aggregates used. PC also has superior fatigue strength compared with conventional Portland cement concrete. PC has also been reported to have excellent bond strength to different substrates including concrete and steel.
The improved mechanical characteristics of PC stem from a tight microstructure which allows PC to have excellent durability as well. The above attractive mechanical and durability characteristics promoted the use of PC as overlays in bridge decks and parking structures. While PC overlays have been used in numerous bridges and parking structures worldwide, they have been reported to suffer fatigue cracks that lead to premature debonding. Methods to improve fatigue strength of PC have been sought.
Carbon nanotubes (CNTs) have been utilized as nanofillers and/or nanoreinforcement to improve the mechanical properties of polymers. CNTs have remarkable strength and stiffness properties and are considered as one of the most attractive materials with very high strength and stiffness to weight ratios. The relatively high aspect ratio of CNTs allows them to improve load transfer in polymer matrices, and as such was reported to significantly improve the tensile and flexural strength and modulus as well as fracture toughness of epoxy.
Furthermore, researchers showed that well dispersed CNTs can significantly improve the electrical conductivity of polymers. This is attributed to the ability of the CNTs to form a network of connected conductive fibers inside the polymer matrix and thus improve its electrical conductivity by a few orders of magnitude. However, the above improvements in polymers using CNTs are conditioned by achieving a good dispersion of CNTs inside the polymer matrix. The very high surface area of CNTs generates strong intrinsic van der Waals forces between individual tubes that cause CNTs to agglomerate in bundles. Agglomerations cause CNTs to have a very low solubility in most solvents, often resulting in a non-homogenous dispersion within a surrounding matrix. Homogenous dispersion is crucial for matrix enhancement, because it increases the surface area of nanotubes that is available for interaction with the matrix. Therefore, it is essential to ensure the homogeneous dispersion of CNTs throughout a composite matrix.
Recently, researchers have improved the mechanical properties of polymer concrete using nanoparticles such as nanoclay, carbon nanotubes, and carbon nanofibers. It was reported the ability to significantly enhance the mechanical and thermal characteristics of performance of UP polymer concrete using nanoclay. Other research has reported a reduction in the flexural strength of PC incorporating nanoclay. It also has been shown that the ability of COOH— functionalized multi-walled Carbon nanotubes (MWCNTs) improve the impact strength of epoxy PC. This improvement was attributed to the ability of functionalized MWCNTs to bond with the epoxy matrix and create a new epoxy-MWCNTs nanocomposite with improved impact and flexural strength.
It has also been long realized that structural collapse of concrete elements under extreme loading events (e.g. earthquakes, hurricane, floods) takes place because of exceeding the displacement and/or strain limits of concrete elements. Concrete ductility, therefore, represents a major challenge necessary to overcome and to prevent the progressive collapse of concrete structures exposed to extreme events. Resilient infrastructure is defined as infrastructure that are designed to survive extreme events and to overcome extreme deformations without observing extreme damage. Developing concretes with extreme ductility is a major step towards resilient infrastructure.